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Besieged areas of Homs have been severely damaged by shelling

Forces loyal to the Syrian government have reportedly killed dozens of rebels who were trying to break an army siege of parts of Homs, in central Syria.

State-owned news agency Sana said troops killed 37 "terrorists" in one operation alone and several others in other attacks.

UK-based activist group the Syrian Observatory for Human Rights said at least 45 rebels were killed.

Syria's civil war has left at least 100,000 people dead.

The army's siege of rebel-held areas in Homs's Old City has lasted more than a year.

Observatory director Rami Abdel Rahman said the number of dead could be higher.

"They were killed as they tried to launch an operation to end the siege of Homs. They were ambushed by regime forces near the Khaldiya neighbourhood, which is under government control," he told AFP news agency.

Several thousand civilians are believed to be trapped by the siege.

In October, activists reported severe food and energy shortages in the besieged areas and warned that residents faced starvation.

Car bomb

The UN has expressed grave concern over reports that over half a million people remain trapped in rural areas around the capital Damascus and there are cases of severe malnutrition among children.

On Thursday the observatory also reported that a car bomb in Kafat in the central province of Hama killed at least 18 people.

State TV also reported the "terrorist" blast, saying 16 people were dead and many more wounded. Much of the province is still under government control.

Meanwhile in the embattled city of Aleppo, government warplanes reportedly carried out fresh air strikes on the rebel-held district of Sheikh Maqsud.

An aerial offensive against rebels in Aleppo using barrel bombs and Scud missiles started last month and has killed hundreds, mostly civilians.

On Wednesday, Russia blocked a UN Security Council statement condemning the air strikes.

Diplomats said Russia put forward amendments to the UK-sponsored statement that removed reference to what had happened in Aleppo.